Holland has excellent advice above. I would also add the following ideas:
1. One of the best tricks to a great lawn is overseeding , as the best way to prevent weeds from getting a foothold is to have a thick and healthy lawn.
2. Next year remember that lawns need on average an inch of water a week. Do not wait for the grass to brown before you start watering - if you go more than four or five days, water that lawn. Also: it is better to get the lawn a deep soaking once every 7-10 days than to lightly water every day. Light watering does not encourage root growth in the lawn, as the plant is not forced to dig deeper, and also weeds (especially crabgrass) love frequent shallow waterings.
3. Set your mower for the correct height: 3" or so is a good level, depending on the variety. If you cut the grass too short you will overstress it. Taller grass also inhibits weed growth.
4. Sharpen your blade several times a year, as a dull blade injures the grass. I have an extra blade that I keep ready to switch out, and I sharpen the one not being used.
5. Use a mulching blade as much as possible, as this puts nutrients back in the soil, helps maintain soil moisture, and keeps weeds down. If you elect to bag your clippings every cutting, at some point you will need to add nutrients. Early in the fall season just run your mower over the leaves and turn them into mulch to help improve soil quality, especially in sandy or clayish soils.
Finally, lawn bragging time. I have not been using fertilizer or weedkillers, just handpulling of weeds and overseeding, plus the above tips. Also, my lawn has five dogs and four grandchildren stomping around: